Aerobic Oxidative Cleavage of Vicinal Diol Fatty Esters by a Supported Ruthenium Hydroxide Catalyst

Oxidative cleavage of fatty acids and fatty acid derivatives can be used to obtained mono- and dicarboxylic acids, which are valuable building blocks in different industries. Although ozonolysis has been industrially developed, there is a need to replace ozone with a more benign oxidant. An alternative process for the oxidative cleavage of dihydroxystearic acid methyl ester 6b using oxygen as an oxidant and a heterogeneous ruthenium catalyst (Ru(OH)(x)/gamma-Al2O3) was studied. Detailed investigations of the formation of intermediates and byproducts as a function of time led us to improve the experimental conditions. 1b was oxidized into the corresponding pelargonic acid 2a and azelaic acid 3a with yields of 85 and 80%, respectively, in a batch reactor with a biphasic organic/aqueous system under 5 bar of oxygen. The reactivities of the different intermediates studied independently under the same experimental conditions enabled us to propose a parallel mechanism for the oxidative cleavage of diol 6b. The recyclability of the catalyst was also studied. Even if Ru traces could be found in the aqueous phase, the observed drop in activity after four runs could be explained by adsorption of byproducts at the surface of the catalyst. The activity could be recovered after washing the catalyst with 0.1 M NaOH under sonication.